The timing of leukemic cell kill by steroids in clones of the human line CEM has been studied. A steroid lysis-resistant CEM clone with functional steroid receptors has been defined. Glutamine synthetase induction is proposed as a marker for functional glucocorticoid receptors in leukemia. By restriction endonuclease analysis growth hormone genes in Gh3 x L cell hybrids are intact but by RNA analysis are not transcribed. DNA methylation plays little role in growth hormone expression. Cell-free transcription of growth hormone genes has been achieved, and vectors developed to study growth hormone gene regulatory sequences. A computer-assisted method for screening cDNA clones has been devised. A method for fixing DNA from bacterial colonies to reusable paper filters has been developed. Human glucocorticoid receptor has been purified and antiserum prepared to it.